1. Field of the Invention
This invention relates to a photomask evaluation method and a manufacturing method of a semiconductor device.
2. Description of the Related Art
The operation of adequately evaluating a pattern becomes more important as the pattern in a semiconductor device such as an LSI is further miniaturized (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. 2002-243428).
When a mask pattern formed on a photomask is evaluated, the pattern dimensions are measured in various portions on the photomask and the average value of the pattern dimensions and dispersion (variation) in the pattern dimension are calculated. Specifically, measurement areas called ROI are set in a plurality of portions on the photomask and the pattern dimensions are derived from the edge profiles of the patterns in the ROIs. That is, distances between the edges are calculated based on the edge profiles and the average edge-edge distance in the ROI is set as the pattern dimension.
However, a variation in the dimension caused by the roughness contained in the edge profile exerts a larger influence on the precision of the dimension as the precision of the dimension is more severely required. Various spatial frequency components are contained in the roughness of the pattern edge and frequency components having periods longer than the ROI width (the area width in a direction parallel to the extending direction of the pattern) are present. Therefore, even if the pattern width is originally set constant, the pattern dimension (edge-edge distance) varies according to the edge roughness. That is, the dimension values obtained depending on the ROI width set at the time of measurement vary. As a result, a variation in the pattern dimension in the mask cannot be precisely evaluated.
If the ROI width which is sufficiently larger than the period of the roughness is set, it becomes possible to avoid the above problem. However, when the ROI width is increased, the edge-edge distances in the ROI are averaged. As a result, a variation in the dimension at the spatial frequency having a long period which exerts a bad influence on the device characteristic will be neglected. Therefore, it becomes impossible to adequately evaluate the pattern.
As described above, if the ROI width (measurement area width) is small, there occurs a problem that the pattern dimension cannot be precisely measured and a variation in the pattern dimension in the mask cannot be adequately evaluated. On the other hand, if the ROI width (measurement area width) is large, there occurs a problem that a variation in the dimension at the spatial frequency having a long period which exerts a bad influence on the device characteristic will be neglected and the pattern cannot be adequately evaluated.